1. Field of the Invention
The present invention relates to a piezoelectric vibrator, and specifically relates to a piezoelectric vibrator having a piezoelectric vibrator element bonded to a casing with support arm parts.
2. Description of the Related Art
For example, in the electronic apparatus such as a cellular phone or a portable information terminal, there is used a piezoelectric vibrator using a quartz crystal or the like as a device used for a clock time source, a timing source for a control signal and so on, a reference signal source, and so on.
As a piezoelectric vibrator of this kind, there has been known a device having a piezoelectric vibrator element hermetically encapsulated in a cavity formed of a package and a lid member as shown in JP-A-2004-297198.
FIGS. 5A through 5F are diagrams showing a structure of a piezoelectric vibrator element 600 of related art.
As shown in FIGS. 5A and 5B, the piezoelectric vibrator element 600 is provided with a base 800 formed of a piezoelectric material and having a predetermined length, and a pair of vibrating arms 700a, 700b extending side by side from the base 800, and at the same time is provided with a pair of fixing arms 900a, 900b extending side by side on the outer side of the vibrating arms 700a, 700b from the both side ends of the base 800.
Further, the piezoelectric vibrator element 600 is fixed by bonding the fixing arms 900a, 900b to an electrode part 1400 provided to the package 200 with electrically-conductive adhesive members 500a, 500b on an imaginary centroidal line passing through the centroid G of the piezoelectric vibrator element 600.
FIGS. 5C through 5F schematically show the displacement in the length direction of the piezoelectric vibrator element with respect to an external force (an external impact) in the case of assuming the fixation place of the piezoelectric vibrator element as a fixed point P.
FIG. 5C shows the piezoelectric vibrator element of the related art in which the piezoelectric vibrator element is fixed (cantilevered) in the base. Since the tip of each of the vibrating arms 700a, 700b is far from the fixed point P, the displacement with respect to the external force is as strong as M1.
In contrast, in the case of the piezoelectric vibrator element 600 shown in FIGS. 5A and 5B, since the fixing arms 900a, 900b are fixed on the centroidal line, by displacing the base side and the tip side in the vertical direction centered on the fixed point P as much as M2 as shown in FIG. 5D, the total displacement M2 becomes smaller compared to M1, which is the displacement of the case of the cantilever structure, and thus, the piezoelectric vibrator element is effectively prevented from colliding with the inside of package 200 to be damaged according to the related art document mentioned above.
However, in reality, as shown in FIG. 5E, the fixed point P is not fixed in the central portion of the vibrating arm 700, but is fixed in the fixing arm 900 via the base 800.
Therefore, as shown in FIG. 5F, only the base 800 side from the fixed point P is displaced as much as M2 similarly to the extended state of a spring, and further, the vibrating arm 700 is displaced as much as M3 pivoted on the base 800 similarly to the case of the cantilever structure. Therefore, since the displacement of M2+M3 occurs at the tip of the vibrating arm 700, it is not necessarily possible to realize the displacement smaller than the displacement M1 of the case of the cantilever structure.
Further, as shown in FIG. 5A, in the piezoelectric vibrator element of the related art, each of the fixing arms 900a, 900b is fixed at one place.
Therefore, since the stress applied to the bonding region becomes high due to the large displacement with respect to the external force as described above, there is a possibility that the bonding region is damaged.
Further, in the case of bonding the fixing arms 900a, 900b, there is a possibility that the piezoelectric vibrator element 600 is tilted in the case of mounting the piezoelectric vibrator element 600 on the soft electrically-conductive adhesive members 500a, 500b, which have not yet cured.
The demand for reducing the displacement of the tip of the vibrating arm and the tilt of the piezoelectric vibrator element with respect to the external force increases as the piezoelectric vibrator is miniaturized so as to have the total length equal to or shorter than 5 mm. In particular, in the case of the size equal to or smaller than 3 mm, it results that the slight increase in displacement and the slight tilt significantly affect the performance of the product and the fabrication yield.